1. Technical Field
The present invention is directed to molded plastic bottles capable of being filled with liquids at elevated temperature. The present invention is particularly directed to such containers having at least two vertically spaced circumferential rows of pressure or vacuum responsive panels.
The present invention particularly relates to blow-molded containers of biaxially oriented thermoplastic materials such as polyethylene terephthalate that are designed to be filled with a hot liquid or semi-liquid product and hermetically sealed, generally referred to as thin-walled, hot-fill containers. The invention pertains to improvements in the design of such containers intended to achieve a container side wall construction that provides enhanced support during filing and subsequent handling and, despite the low weight of polymer used to form the container, retains the desired container configuration despite the development of a partial vacuum within the container when capped and cooled.
2. General Background
It is well recognized that the exposure of any plastic container to elevated temperatures tends to soften the plastic material and make the container less resistant to deformation. It is also well known to thermally treat some plastic containers during manufacturing so that this tendency is diminished to the point that the containers do not deform when hot-filled. Such thin-walled, hot-fill containers are typically used for packaging beverages and other food products that must be placed in the container while hot, the containers being quickly capped to preserve the quality of the contents. During the filling process, the container and head space gasses are subjected to temperatures from the hot product. The container is capped container is then cooled at least to ambient temperature, and perhaps refrigerated, which causes the liquid contents and any head space gases to contract. This is reflected in a drop in internal pressure, or the development of an internal vacuum within the container, which can deform the container. It is well known to compensate for the temperature induced pressure change by providing the container with a plurality of panels having sufficient flexibility and/or elasticity to permit a change in container volume that will at least partially compensate for the pressure changes.
Alberghini et al. U.S. Pat. No. 5,054,632 discloses a container that is intended to be hot-filled including at least two circumferential rows of essentially square panels providing controlled volumetric reduction of the container. A land or post separates each adjacent pair of panels in each row. The rows of panels are staggered with respect to each other such that the lands or posts of one row are vertically aligned with the center of the panels of any adjacent row. The design is said to distribute circumferentially the vertical and horizontal support for any label applied to the label panel of the container while still providing the desired panel movement in response to the existence of a partial vacuum within the container due to hot filling.
Krishnakumar et al. U.S. Pat. Nos. 5,178,289 and 5,279,433 disclose hot-fill containers having a plurality of vertically elongated vacuum panel regions that are symmetrically disposed about a horizontal centerline of the container label panel. They also disclose hot-fill containers having a plurality of vertically paired, generally square vacuum panel regions that are symmetrically disposed about a horizontal centerline of the container label panel. Vertical stiffening ribs are provided between horizontally adjacent vacuum panel recesses or pairs. Additional vertical stiffening ribs are provided in the center of islands or spot label areas within the pairs of vacuum panel regions. The angular extent of the vacuum panel regions and spot label areas is said to be variable to adjust the resistance to barreling and/or to provide a squeezable container.
Darr U.S. Pat. No. 5,690,244 discloses a unitary plastic bottle having a central axis, an upper dispensing end, a lower freestanding base, and a generally round side wall having upper and lower extremities respectively connected to the upper dispensing end and the lower freestanding base. The side wall of the container has at least three vertically spaced horizontal ribs of an annular shape extending around the container. The side wall also has at least twelve vertical ribs spaced circumferentially and extending between the horizontal ribs and cooperating therewith to define at least twelve essentially square panels spaced around the container between each adjacent pair of horizontal ribs, and the panels being capable of flexing inwardly to accommodate for shrinkage upon cooling after hot filling of the container.
Ota et al U.S. Pat. No. 6,575,320 discloses a container suitable for hot-fill use with a body having a pair of body portions that are arranged in a longitudinal direction of the body one above the other. Each body portion has a substantially regular polygonal cross-section defined by a plurality of generally flat walls. The generally flat walls of each of the body portions include flexible walls and less-flexible walls, which are arranged alternately to each other in a circumferential direction of the body. When the container is filled with liquid contents at a high temperature and subsequently cooled to room temperature, a resultant pressure drop within the container is absorbed by the walls, initially by a primary inward deflection of the flexible walls and subsequently by a secondary inward deflection of the less-flexible walls.
Despite the variations disclosed in the prior art, there is a continuing need for an improved molded plastic container having a side wall that exhibits outstanding dimensional stability under the typical conditions experienced during and subsequent to hot-fill and capping. In particular there is a continuing need for such a container that will provide sufficient side wall stability and support to inhibit buckling in the event of side wall impact and will provide a more stable feel to the user of the container.